MEXICO CITY — It has become a regular occurrence, particularly around the Easter holiday: scores or even hundreds of Central American migrants making their way north by foot and vehicle from southern Mexico. …

Called “caravans,” most of the journeys, which date back at least five years, have moved forward with little fanfare, virtually unnoticed north of the border with the United States. But tweets by President Trump have suddenly turned the latest caravan into a major international incident and the most recent flash point in the politics of immigration in the United States….

On Monday, he warned that “our country is being stolen” by illegal immigration, blaming Democrats for weak border policies and urging Mexico to strengthen its border enforcement.

“Mexico has the absolute power not to let these large ‘Caravans’ of people enter their country,” he said in a tweet.

In interviews on Monday, the caravan’s organizers sounded frustrated, exhausted and dismayed.

“We are not terrorists,” said Irineo Mujica, Mexico director of Pueblo Sin Fronteras — People Without Borders — a transnational advocacy group that is coordinating the current caravan and has organized others in recent years.